If this is the case, try to create a rule in the firewall that allows all traffic to Windows Update without using the proxy. Then navigate to the following key: [HKEY_LOCAL_MACHINE\System\Current Control Set\Services\Tcpip\Parameters\ Interfaces\[Adapter ID]] Create a new DWORD value, or modify the existing value, called “MTU” and set it to a decimal value like 1492. If it did not help, change the MTU to 1500 and try again.